概述

netty版本：4.1.45

使用netty搭建一个简单的文件服务器，使用HTTP协议对外提供服务。

如果文件不存在，返回403响应码。如果是文件夹，以超链接展示，如果是文件，支持下载。

服务器编码

/**
 *  netty  http 文件下载 服务器
 */
public class MyHttpFileBrowserServer {

    int port;

    public MyHttpFileBrowserServer(int port) {
        this.port = port;
    }

    public void start() throws Exception {
        ServerBootstrap bootstrap = new ServerBootstrap();
        EventLoopGroup boss = new NioEventLoopGroup();
        EventLoopGroup work = new NioEventLoopGroup();
		try {
            bootstrap.group(boss, work)
                    .handler(new LoggingHandler(LogLevel.DEBUG))
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new HttpBrowserServerInitializer());

            ChannelFuture f = bootstrap.bind(new InetSocketAddress(port)).sync();
            System.out.println("http server started . port : " + port);
            f.channel().closeFuture().sync();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            boss.shutdownGracefully();
            work.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        MyHttpFileBrowserServer server = new MyHttpFileBrowserServer(8080);// 8081为启动端口
        server.start();
    }
}

class HttpBrowserServerInitializer extends ChannelInitializer<SocketChannel> {

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {
        ChannelPipeline pipeline = channel.pipeline();
        pipeline.addLast(new HttpServerCodec())// http 编解器
                // http 消息聚合器  512*1024为接收的最大contentlength
                .addLast("httpAggregator", new HttpObjectAggregator(512 * 1024))
                // 支持异步发送大的码流(大的文件传输),但不占用过多的内存，防止java内存溢出
                .addLast("http-chunked", new ChunkedWriteHandler())
                .addLast(new HttpBrowserRequestHandler());// 请求处理器
    }
}

注意这里channelpipeline中的HttpObjectAggregator和ChunkedWriteHandler。

HttpObjectAggregator：用于HTTP消息聚合，将多个消息转换为单一的FullHttpRequest和FullHttpResponse。因为HttpServerCodec解码器在每个HTTP消息中会生产多个对象：HttpRequest、HttpResponse、HttpContent、LastHttpContent。
ChunkedWriteHandler：支持异步发送大的码流(大的文件传输),但不占用过多的内存，防止java内存溢出。

文件服务器业务代码

HttpBrowserRequestHandler是业务代码的核心逻辑。用于检验请求的正确性，遍历文件列表，并以只读的方式读取文件，以流的方式发送到客户端。

这里只是实例代码，功能不是很完善。


class HttpBrowserRequestHandler extends SimpleChannelInboundHandler<FullHttpRequest> {

    @Override
    public void channelRead0(ChannelHandlerContext ctx, FullHttpRequest request) throws Exception {
        // 解码失败 400
        if (!request.getDecoderResult().isSuccess()) {
            sendError(ctx, HttpResponseStatus.BAD_REQUEST);
            return;
        }
        // 只支持get方法
        if (request.getMethod() != HttpMethod.GET) {
            sendError(ctx, HttpResponseStatus.METHOD_NOT_ALLOWED);
            return;
        }
        //
        final String uri = request.getUri();
        // 处理Uri地址
        final String path = sanitizeUri(uri);

        if (path == null) {
            sendError(ctx, HttpResponseStatus.FORBIDDEN);
            return;
        }
        File file = new File(path);
        // 如果文件不存在，或不可访问
        if (file.isHidden() || !file.exists()) {
            sendError(ctx, HttpResponseStatus.NOT_FOUND);
            return;
        }
        // 如果请求是文件夹
        if (file.isDirectory()) {
            // 请求以 '/'结尾，列出该文件夹下的所有内容
            if (uri.endsWith("/")) {
                sendListing(ctx, file);
            } else {
                // 否则自动补全'/' 然后再重定向访问
                sendRedirect(ctx, uri + '/');
            }
            return;
        }

        if (!file.isFile()) {
            sendError(ctx, HttpResponseStatus.FORBIDDEN);
            return;
        }
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile(file, "r");// 以只读的方式打开文件
        } catch (FileNotFoundException fnfe) {
            sendError(ctx, HttpResponseStatus.NOT_FOUND);
            return;
        }
        long fileLength = randomAccessFile.length();
        // 创建一个默认的Http响应
        HttpResponse response = new DefaultHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
        // 设置响应文件大小
        HttpUtil.setContentLength(response, fileLength);
        // 设置 content Type
        setContentTypeHeader(response, file);
        // 设置 keep alive
        if (HttpUtil.isKeepAlive(request)) {
            response.headers().set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);
        }
        ctx.write(response);

        //通过Netty的ChunkedFile对象直接将文件写入发送到缓冲区中
        ChannelFuture sendFileFuture = ctx.write(new ChunkedFile(randomAccessFile, 0, fileLength, 8192), ctx.newProgressivePromise());
        sendFileFuture.addListener(new ChannelProgressiveFutureListener() {
            @Override
            public void operationProgressed(ChannelProgressiveFuture future, long progress, long total) {
                if (total < 0) { // total unknown
                    System.err.println("Transfer progress: " + progress);
                } else {
                    System.err.println("Transfer progress: " + progress + " / " + total);
                }
            }

            @Override
            public void operationComplete(ChannelProgressiveFuture future) throws Exception {
                System.out.println("Transfer complete.");
            }
        });
        ChannelFuture lastContentFuture = ctx.writeAndFlush(LastHttpContent.EMPTY_LAST_CONTENT);
        //如果不支持keep-Alive，服务器端主动关闭请求
        if (!HttpUtil.isKeepAlive(request)) {
            lastContentFuture.addListener(ChannelFutureListener.CLOSE);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        if (ctx.channel().isActive()) {
            sendError(ctx, HttpResponseStatus.INTERNAL_SERVER_ERROR);
        }
    }

    private static final Pattern INSECURE_URI = Pattern.compile(".*[<>&\"].*");

    /**
     * 格式化uri并且获取路径
     *
     * @param uri
     * @return
     */
    private String sanitizeUri(String uri) {
        try {
            uri = URLDecoder.decode(uri, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            try {
                uri = URLDecoder.decode(uri, "ISO-8859-1");
            } catch (UnsupportedEncodingException e1) {
                throw new Error();
            }
        }
       if (!uri.startsWith("/")) {
            return null;
        }
        uri = uri.replace('/', File.separatorChar);
        if (uri.contains(File.separator + '.') || uri.contains('.' + File.separator) || uri.startsWith(".")
                || uri.endsWith(".") || INSECURE_URI.matcher(uri).matches()) {
            return null;
        }
        return System.getProperty("user.dir") + File.separator + uri;
    }

    private static final Pattern ALLOWED_FILE_NAME = Pattern.compile("[A-Za-z0-9][-_A-Za-z0-9\\.]*");

    private static void sendListing(ChannelHandlerContext ctx, File dir) {
        FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK);
        response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/html; charset=UTF-8");
        StringBuilder buf = new StringBuilder();
        String dirPath = dir.getPath();
        buf.append("<!DOCTYPE html>\r\n");
        buf.append("<html><head><title>");
        buf.append(dirPath);
        buf.append(" 目录：");
        buf.append("</title></head><body>\r\n");
        buf.append("<h3>");
        buf.append(dirPath).append(" 目录：");
        buf.append("</h3>\r\n");
        buf.append("<ul>");
        buf.append("<li>链接：<a href=\"../\">..</a></li>\r\n");
        for (File f : dir.listFiles()) {
            if (f.isHidden() || !f.canRead()) {
                continue;
            }
            String name = f.getName();
            if (!ALLOWED_FILE_NAME.matcher(name).matches()) {
                continue;
            }
            buf.append("<li>链接：<a href=\"");
            buf.append(name);
            buf.append("\">");
            buf.append(name);
            buf.append("</a></li>\r\n");
        }
        buf.append("</ul></body></html>\r\n");
        ByteBuf buffer = Unpooled.copiedBuffer(buf, CharsetUtil.UTF_8);
        response.content().writeBytes(buffer);
        buffer.release();
        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }

    private static void sendRedirect(ChannelHandlerContext ctx, String newUri) {
        FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.FOUND);
        response.headers().set(HttpHeaderNames.LOCATION, newUri);
        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }

    private static void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
        FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, status,
                Unpooled.copiedBuffer("Failure: " + status.toString() + "\r\n", CharsetUtil.UTF_8));
        response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain; charset=UTF-8");
        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
    }

    private static void setContentTypeHeader(HttpResponse response, File file) {
        MimetypesFileTypeMap mimeTypesMap = new MimetypesFileTypeMap();
        response.headers().set(HttpHeaderNames.CONTENT_TYPE, mimeTypesMap.getContentType(file.getPath()));
    }
}